| Summary: | <p>Abstract</p> <p>A male patient, born to unrelated Belgian parents, presented at 4 months with epistaxis, haematemesis and haematochezia. On physical examination he presented petechiae and haematomas, and a slightly enlarged liver. Serum transaminases were elevated to 5-10 times upper limit of normal, alkaline phosphatases were 1685 U/L (<720), total bilirubin was 2.53 mg/dl (<1.0), ammonaemia 69 μM (<32), prothrombin time less than 10%, thromboplastin time >180 s (<60) and alpha-fetoprotein 29723 μg/L (<186). Plasma tyrosine (651 μM) and methionine (1032 μM) were strongly increased. In urine, tyrosine metabolites and 4-oxo-6-hydroxyheptanoic acid were increased, but succinylacetone and succinylacetoacetate - pathognomonic for tyrosinemia type I - were repeatedly undetectable. Delta-aminolevulinic acid was normal, which is consistent with the absence of succinylacetone. Abdominal ultrasound and brain CT were normal.</p> <p>Fumarylacetoacetase (FAH) protein and activity in cultured fibroblasts and liver tissue were decreased but not absent. 4-hydroxyphenylpyruvate dioxygenase activity in liver was normal, which is atypical for tyrosinemia type I. A novel mutation was found in the FAH gene: c.103G>A (Ala35Thr). <it>In vitro </it>expression studies showed this mutation results in a strongly decreased FAH protein expression.</p> <p>Dietary treatment with phenylalanine and tyrosine restriction was initiated at 4 months, leading to complete clinical and biochemical normalisation. The patient, currently aged 12 years, shows a normal physical and psychomotor development.</p> <p>This is the first report of mild tyrosinemia type I disease caused by an Ala35Thr mutation in the FAH gene, presenting atypically without increase of the diagnostically important toxic metabolites succinylacetone and succinylacetoacetate.</p>
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